Control apparatus



March 1961 J. P. KRIECHBAUM 2973630 CONTROL APPARATUS Filed May :s 1957 ICE BANK 25 ONTROLLER MOTOR AND COMPRESSOR T JOHN P. KRIECHBAUM AT 7URIVE Y IN VEN OR United States Patent 2,973'630 CONTROL APPARATUS John P. Kriechbaum, Minneapolis, Minn., assignor "Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware The present invention is direeted to temperature sensitive control devices and particularly to such devices in which control is eflected by volume changes caused by melting and freezing of a substance contained in a temperature sensing chamber.

Control devices of this type find utility in maintaining a layer of ice of the desired thickness on an evaporator coil submerged in a tank of water. A sensing element filled with water is located approxirnately at the desired ice level and it is intended that the water within the element be frozen when the element is covered with ice and melted when water surrounds the element. By building up an ice bank during periods of light load, a refrigerating system of moderate size is able to handle intermittent heavy loads.

Erratic opcration and undesirable short cycling has been experienced with controls of this type in the past. This has been due to inability cf the sensing element to ditferentiate between watcr and ice at the melting temperature, and is also due tothe melting pointof the ice withinthe sensing chamber being slightly less thaxithe ice of the ice bank. This latter effect is due primarily to pressure maintained on the sensingelement by the switch mechanisrn actuated thereby, and secondarily to any impurities that may be contained in the element fill.

'According to the present invention the refrigerating systern is controlled by a sensing element having a fill that melts and contracts to close an associated switch at a temperature slightly above the melting point of the ice bank. The fill can be controlled to freeze and expand .to open the switch at a temperature slightly below=the normal freezing temperature of the ice of the ice bank.

ment must be embedded in the ice bank 10 -a depthat which the temperati1re gradient between the ice surface and the evaporation coil equals the freezing temperature of the fill. When the refrigeration system -is stopped, the temperature of the ice bank will equalize at the melting temperature, but the element fill will remain frozen until the eleme'nt is clear or substantially clear of the ice becausethe fill melts at a temperature slightly above the ice melting temperature. When the water surrounding In order 110 attain this low temperature the sensing elethe element is definitely above the freez-ing point the fill willmeltto start the compressor. Since the element fill melts above the melting point of ice and freezes below the freezing point of water, thethickness of the -ice bank is controlled with sufficient accuracyand withic:e

Also, according to the invention, it is proposed that an additive be mixed with water in a ratio to provide an element fill having a melting point slightly above the melting point of pure water. lt has been found that a very small amount cf deuterium Oxide (commonly known as heavy Water) added to water provides a mix ture that melts slightly above 32 F. This mixture provides a fill whose melting and freezing points are closely related to the melting and freezing points of pure water but higher. All other known materials when mixed with pure water result in lower melting and freezing points.

The water in the open tank will freeze at 32 F. since an ice surface exists at which the freezing takes place. This is not true of the water in the -sensing element, however, and considerable super-cooling takes place before freezing occurs. Thus, if no icefis present in the sensing element it must be cooled to some temperature below 32 F. before freezing Will star t. The amonnt of supercooling is controlled by various means including insertion of si-lver -iodide crystals in the element as has been known heretofore.

It istherefore an object of the present invention to -provide an improved temperature control systern.

. ice.

These and other objects will become apparent upon a study of the specification and drawings of which:

Figure 1 is a schematic view of a temperature controller when used to maintain an ice bank in a milk storage installation.

Figure 2 is a cutaway view of the ice bank controller shown in Figure 1.

Referring to Figure l, a temperature control device 10, having a remotely -located sensingelernent 11 counected thereto by a capillary 12, is shown as used in an ice bank control installation for mziintaining a predeterrnined amount of ice around the c0ils of'a refrigeration apparatus. The particular installat ion shown is for illustrative purposes only and has an evaporator coil the tank and the heat is expelled from condenser 20 as air, is passed therethrough by a fan 22. Controller 10 is conn6cted by wires 23 and 24 to control the motor. The 'sensing element 11, through controller 10, controls the compressor to maintain an ice bank 25 of a predetermined thickness on the coils. This ice bank is a means of storing cooling capacity for cooling a second inner tank.

Referring to Figure 2 the controller 10 is shown in more detail. It has a snap switch 31 having an operating plunger 32 which is engaged by a lever 33. The lever is pivoted at one extremity 011 a shaft 34. A spring 35 is attached to lever 33 to bias it upward in a oourlterclockwise direction about pivot 34 to engage the plunger 32 of.the switch. A second spring 40 is coiled about an adjustment nut 41.. Spring 40 is lodged between the upper portion of the casing 42 and a collar 49 carried on' bell-shaped p r n4 n 4l h= 9 989 thereof. Collar 49 provides a-friction-load-on-nut4l to shaft 44 through nut-4l' by spring 40. The lower end 43 of nut 41 contacts a raised po'rti0n 51 of lever 33. When the diaphragm45 is moved upward the nut 41 compresses spring 40 to allow lever 33 to move upward under the force of spring35 pushing the plunge;r 32 o-f the switoh upward. By the adjustment of n't1t' 41, the device is calibrated and the switch Will operate for a predetermined movement ofdiaphragm 45.

Sensor 11 contains a diaphragm 46 to separate the unit into two chambers. Chamber 47 is connected to tube 12. The liquid fill used in chamber 47, tube 12, and below the diaphragm of operating head '50 has a relatively low freezing point. It is used only to transrriit the force of the sensing element 11 to controller 10. Chamber 48 is filled with a liquid fill 60. When the liquid 60 in chamber 48 freezes, a pressure is developed which is reflected through the capillary tube to diaphragm 45 to operate the switch.

Liquid fill 60 comprises a liquid such as water with a predetermined percentage of deuterium-oxide (D which is eommonly known as heavy water. Deuteriumoxide When added to a liquid such as Water has the characteristic of increasing its freezing point above the normal freezing point of water alone. For example, a solution of water might be made with deuterium-oxide .to have a freezing point of 32.3 F. After this -solution is added to the device it Will generally pick up impurities as a result oft the normal handling during the manufac- 'turing process which. for example, might reduce the freezing point to 32.2 F. Further, it has been found in a pressure developing oontrol device of this sort the pressure in the sensing element as a result of the freezing cf the liquid is sufiicient to further reduce the freezing point of this specified mixture to 32.1 F. This is an irnprovement over the prior art as heretofore with water fills the impurities and pressure tends to reduce the freezing point below the freezing point of pure water at 32 F.

Operation Referring toFigure 2 it is assumed that the control has operated the switch 31 to energize thefassociated motor eompressor unit and the evaporator coil 13 is cold, for example, around 20 F. There will be a temperature diiferential between the evaporator coil and the water bounding the edge of the ice bank at 70 as the water will be 32 F. or above. As long as the controller sensing element 11 is in contact with water, as shown, its temperature will rernain around 32"F., thus, there will be a temperature gradient between the under side of the element 11 and the evaporator coil from 20 F. to 32 F. As soon as the ice bank starts to form on the right side of the element, the element temperature will drop and it will be between the extreme temperatures of 20 F. and 32 F. As the ice bank continues to form, the temperature of the element willdrop until the solution therein begins to freeze to develop a pressure on diaphragm 45 to operate the svwitch and turn the compressor oft. The freezing temperature depends upon the amount of super-cooling and as mentioned it can be controlled and even reduced to zero so that the freezing and melting point of the fill is the same.

When a control o-f this type is us'ed in a bulk milk tank apparatus as shown in Figure l, the ice bank is normally not expected to be maintained over a 12 hour period due to the frequency of the milking period. Assuming no ice is formed 011 the coil, the refrigeration apparatus is placed in operation. As theice formkad arouhd the sensitxg element as shown in"Figt1re' 2 the temperature of the -sensingelement drops. Since there is no ice in the chamber 48, the freezing -:-point of the fluid is much lower than 32 due to the super-cooling phenomenon. In some cases, the ice bank may build two inches beyond the element before the refrigeration apparatus is shut ofi. Since a temperature gradientyexists between cooling coil 13 and the edge of the ice bank 70, the element may be several degrees below 32 F. -before the fluid in chamber 48 freezes to turn 01T the refrigeratidn apparatus. As theevaporator coil ceases to take heat from the ice, the temperature of the ice bank Will increase and it has been found to approach a uniform temperature of around 32 F. At this time the sensing element which is embedded in the ice banlvwould be at 32 F. 'It is obvious that if the melting point of the liquid therein was below 32 F., as in controls of the prior art, the ice forrned in element 11 would melt to again turn on.the compressor.

'As soon as the compressor was turned on, the evaporator coil would again start cooling the ice bank and re-establish the gradient across the bank until the ice in the element again forms to* shut olf the compressor. Such a phenomena results in short cycling of the compressor which is not desired.

When the warm milk is poured into the tank 26, the ice bank is normally melted complete-ly away from the sensing element; in fact, the equipment manufacturer generally designs the capacity of the equipment so the ice bank is completely used each time the tank is filled With warm milk. Under such conditions, the ice would be completely melted in chamber 48, and upon the ice bank being again formed on the cooling coil, the supercooling phenomenon takes place again and the ice builds up the element.

Normally the control device is not used where the ice bank is only partially melted back to uncover the element 11; however, if such a condition should take place, the ice in chamber 48 rnay not completely melt. Upon a subsequent operation of the refrigeration apparatus, the ice bank forms on the cooling coil until the element is substantially covered as shown in Figure 2. Since the super-cooling phenomenon did not take place as ice already exists in chamber 48, a differentiell is maintained by the diflerence in freezing point of the fluid in chambe'r 48 as brought about by the difference in pressure needed to operate the control device 10. When the refrigeration apparatus is operating and the ice bank is being formed, a freezing point slightly below 32 exists in chamber 48 so the element 11 must be substantially covered With ice before the fluid in chamber 48 freezes. Once the refrigeration apparatus is turned 0fi, a different pressure in chamber 48 is needed to reenergize the refrigeration apparatus by controller 10. In other words, a slightly higher melting point of the fluid in chamber 48 exists When the fluid in chamber 48 is mkalting t0 energize the refrigeration apparatus. The slightly higher melting point is probably above 32 if the deuterium oxide is used. Without the deuterium oxide, the melting temperature would be below 32, and the refrigeration apparatus would be turned on as soon as the ice bank reached the uniform temperature around 32. The short cycling condition is eliminated by the use of deuterium oxide.

With the improved fill used in the sensing element, the freezing point is slightly above 32 F. and the ice in the element does not melt until the ice bank reduces in size sufficiently to expose the element to the water so that the element temperature can increase above 32 F.

As stated before, in the manufacturing of such a device the amount cf impurity has a great effect upon the freezing temperature of the liquid fill. By the use of this deuterium-oxide it is possible to anticipate the possible percentage of impurities and to compensate for the possible reduction in the fill temperature due to the Another advantage of this improved fill is that it has possibly less tendency to super-cool than the normal fills heretofore used. In the initial operation of the device as the ice bank is forming around the element 11 it has been found, with conventional fills, that the element temperature often drops much lower than the freezing point of the liquid therein and yet the liquid does not freeze. As super-cooling depends on so many fact-ors the freezing temperature can vary which causes van'ations in the thickness cf the ice bank. T0 lessen tnis, crystals are often added to control and stabilize the amount of super cooling as it greatly affects the control results of such a temperature control device.

While the invention has been described in connection with a temperature control device for controlling the ice bank in a storage container, it is obvious that the invention may be used in -other applications and therefore it is intended that the present invention only be limited by the scope of the appended claims-4n which I claim:

1. In a oontrol system for controlling the size of an ice bank maintained on the evaporat-or coil of a refrigeration apparatus which are submerged in water, a switch for controlling the operation of the refrigeration apparatus, a pressure sensitive switch operator for operating said switch, a sensing element having a first and a second chamber separated by a flexible Wall, said sensing element being attached to the evaporator coil, conduit means connecting said first chamber and said pressure operator in a closed liquid filled system so that upon the compressi-on of said liquid a predetermined amount in said first chamber said operator causes said switch to stop the operation of the refrigeration apparatus, a fluid expanding upon freezing and having a freezing point and a. melting point above 32 F. said fluid being used to fill said second chamber so that upon said sensing element being covered with ice and being exposed to a temperature below 32 F. said fluid will freeze to expand and apply a compressing force through said wall to said fill and thus operate said switch shutting down the refrigeration apparatus, said refrigeration apparatus being reenergized when said element is substantially uncovered.

2. In a control system for controlling the size of an ice bank maintained on a cooling coil submerged in water of a cooling apparatus, a switch for controlling the operation of the cooling apapratus, a pressure sensitive switch operator for operating said switch, a sensing element having a chamber filled with fluid having a freezing temperature slightly above the freezing temperature of water, said element being adapted to be mounted adjacent the cooling coil in the water, means connecting said element to said operator whereby, upon said fluid expanding as it freezes as the ice bank surrounds said sensing element v to produce a pressure in said chamber, said switch is operated to deenergize the cooling apparatus, said fluid ation ofthe cooling apparatus, a pressure sensitive switch operator for operating said switch, a sensing element having a chamber filled with fluid, said element being adapted to be mounted adjacent the cooling coil in the water, means connecting said element to said operator whereby upon said fluid expanding as it freezes as the ice bank surrounds said sensing element to produce a pressure in said chamber, said switch is operated to deenergize the cooling aparatus, said fluid having a freezing and melting temperature slightly above the freezing temperature of water, said fluid freezing as the ice bank surrounds said sensing element at a predetermined temperature above the freezing temperature of the water even though the fluid is under a pressure upon increasing in volume as the temperature gradually decreases, said fluid having a melting point above the freezing point of water even though the pressure created by said fluid when frozen.

would normally reduce the freezing point whereby said cooling apparatus is not reenergized lintil the ice surrounding said element is removed to raise the temperature of the element above said predetermined freezing temperature of water.

4. A sensing element adapted to be mounted adjacent a cooling coil of an ice bank controlling apparatus wherein an ice bank is maintainecl on a cooling coil submerged in a water tank, comprising, a chamber filled with a fluid which upon expanding produces a pressure in the chamher, means adapted to control the temperature of the cooling coil in response to the pressure developed in said charnber, said fluid comprising deuterium oxide and water, said fluid having a freezing temperature above the freezing temperature of water so that the efiect of the pressure developed in said chamber when said fluid freezes to increase in volume does not lower the freezing 0r melting temperature below the freezing temperature of the water.

5. A thern1al sensing unit for controlling the size of an ice bank on a heat exchanger comprising, a chamber filled with a fluid so that upon said fluid freezing to increase in volume a condition indicative cf the temperature is obtained, means responsive to said increase in volume and the resultant pressure developed in said chamber ad2ipted to control the capacity of the heat exchanger, said fluid cornprising water and deuterium oxide whereby said fluid freezes and melts at a temperature above the freezing point cf water alone and the efrect of said pressure on said fluid to lower the freezing point is overcorne.

6. A therrnal sensing unit comprising, a chamber filled with a fluid so that upon said fluid freezing to increase in volume a pressure indicative of the temperature is obtained, said fluid comprising water and deuterium oxide whereby said fluid freezes at a temperatu're above the freezing point of water alone and the elfect of pressure on said fluid which results in the lowering of the freezing point of the fluid is reduced.

References Cited in the file of this patent UNITED STATES PATENTS v 1,719,851 Raney July 9, 1929 2,187258 Wood Jan. 16, 1940 2,622,923 Cobb Dec. 23, 1952 2,724950 Rothwell Nov. 29, 1955 

